16/11/2025
🌕Proximal isovelocity surface area (PISA):
The proximal isovelocity surface area (PISA) radius method is the most recommended quantitative approach for MR severity assessment, whenever feasible.
This method has been widely used and validated in numerous studies.
The 3 principles of PISA:
1) When liquid flows from a large chamber through a smaller or***ce at a fixed rate, flow velocity increases to a point at which it is greatest as it converges on the narrowest region of the flow. When the or***ce is rounded and narrow, this flow convergence occurs in a hemispherical geometry with a velocity that is equal throughout the hemisphere surface and is referred to as the proximal isovelocity surface area (PISA).
2) For any given or***ce, flow equals area of the or***ce times velocity. Thus, regurgitant flow = regurgitant or***ce area X velocity of the regurgitant jet.
3) Mass conservation law: Flow across any isovelocity surface = flow through or***ce. The rate of flow throughout the convergent shells and regurgitant or***ce (effective regurgitant or***ce area EROA) is equal (volume does not alter with changing geometry, only velocity changes)
Flow across PISA = Flow across EROA
The flow rate through the or***ce (mL/s) can be calculated by multiplying the surface area of the hemisphere (2πr2) by the Nyquist velocity at that point (the aliasing velocity selected (Va) so
Mitral regurgitant flow = Flow across any isovelocity surface = PISA = 2 π r2 × Va
Based on these 3 principles:
A) The effective regurgitant or***ce area (EROA, in cm2) can then be calcluated by dividing the mitral regurgitant flow (PISA x Va) by the corresponding peak MR velocity (V max in cm/s) based on the conservation of mass law.
(EROA = 2πr2 × Va/Vmax)
B) The regurgitant volume (R vol) can be calculated as the product of EROA and the velocity time integral (VTI) of the MR jet, and regurgitation fraction (RF) as Regurgitation volume divided by total stroke volume.
👨🏽⚕️PISA assessment:
🔀The apical 4C view is recommended for optimal visualization of the PISA radius, but the parasternal long-axis view can also be used, especially in regurgitant jets directed posteriorly.
🔀These flow convergence hemispheres are better identified on echo by reducing the color flow velocity at which blood flow aliases (Nyquist limit) to between 20 and 40 cm/s in the direction of the flow. Doing so identifies the hemisphere moving at our selected velocity in the direction of the or***ce and allows measurement of the hemisphere height. Since flow velocity increases as blood approaches the regurgitant or***ce, the relationship between PISA radius and Nyquist limit is inverse (PISA height increases as the Nyquist limit is reduced). PISA It is recommended that multiple acquisitions are made by slowly rotating between the A4C view and the A3C view while keeping the MR jet in focus.
🔀The PISA radius is measured in mid-systole using the first aliasing in the centre of the flow convergence region. Careful scanning is needed to align the CW Doppler interrogation line with the direction of the jet to avoid underestimation of the maximum regurgitant jet velocity.
🔀Calculate PISA= 2 π r2
🔀 Calculate EROA= PISA x Va/ Vmax
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